Java 设计模式-备忘录模式

模式介绍

备忘录模式（Memento Pattern）保存一个对象的某个状态，以便在适当的时候恢复对象。备忘录模式属于行为型模式。

使用场景

1、需要保存、恢复数据的相关状态场景。
2、提供一个可回滚的操作。

系统实现

/**
 * 记录对象状态的类
 */
public class Memento {
   private String state;
 
   public Memento(String state){
      this.state = state;
   }
 
   public String getState(){
      return state;
   }  
}

/**
 * 需要保存状态的类
 */
public class Originator {
   private String state;
 
   public void setState(String state){
      this.state = state;
   }
 
   public String getState(){
      return state;
   }
 
   public Memento saveStateToMemento(){
      return new Memento(state);
   }
 
   public void getStateFromMemento(Memento Memento){
      state = Memento.getState();
   }
}

import java.util.ArrayList;
import java.util.List;
/**
 * 保存对象各种状态集合的类
 */ 
public class CareTaker {
   private List<Memento> mementoList = new ArrayList<Memento>();
 
   public void add(Memento state){
      mementoList.add(state);
   }
 
   public Memento get(int index){
      return mementoList.get(index);
   }
}

/**
 * 客户端
 */ 
public class Client {
   public static void main(String[] args) {
      Originator originator = new Originator();
      CareTaker careTaker = new CareTaker();
      originator.setState("State #1");
      careTaker.add(originator.saveStateToMemento());
      originator.setState("State #2");
      careTaker.add(originator.saveStateToMemento());
      originator.setState("State #3");
      System.out.println("Current State: " + originator.getState());    
      originator.getStateFromMemento(careTaker.get(0));
      System.out.println("First saved State: " + originator.getState());
      originator.getStateFromMemento(careTaker.get(1));
      System.out.println("Second saved State: " + originator.getState());
   }
}
结果：
Current State: State #3
First saved State: State #1
Second saved State: State #2